Fishnet beacon

From HFUnderground

Fishnet beacons, also known as Drift Nets, Fishing Buoy Transmitters, Radiobuoys, Radio Buoys, Radio-Buoys, and Fishnet Buoys are low power transmitters which periodically send CW identifiers followed by a carrier. The average repetition rate is about 4 minutes. They are battery powered and use fairly small and inefficient antenna, however they can be heard for hundreds or even thousands of miles. Fishnet beacons are can be found between 1.6 and 4 MHz, and are most often found in and above the 160-meter amateur radio band (1800-2000 kHz or 1.8-2 MHz) They are typically used by fishermen to locate nets, hence the name.

There are reports of similar beacons operating in the 26-30 MHz range (including inside the 11 meter CB band and 10-meter amateur band). They follow a very similar format, transmitting a varying-number of characters ID with low power. Similar ocean-based telemetry systems use frequencies in the 26 MHz to 30 MHz range, including Marine Instruments Radio Buoys (authorized for 26145 kHz, 26150 kHz, 26155 kHz, 26160 kHz, 26165 kHz, 26170 kHz and 26175 kHz) and Datawell Waverider telemetry buoys (authorized for 29710 kHz, 29730 kHz, 29750 kHz, 29770 kHz and 29790 kHz per FCC waivers). Outside of the United States similar systems use various frequencies in the 1.6 to 4 MHz band and the 25 to 30 MHz band.